1. Field of Invention
This invention relates generally to maintenance stations for fluid ejection system.
2. Description of Related Art
In a thermal fluid ejector, the power pulses that result in a rapidly expanding gas bubble to eject the fluid from the nozzle are usually produced by resistors. Each resistor located in a respective one of a plurality of channels. Each resistor is individually addressed by voltage pulses to heat and vaporize fluid in the channels. As voltage is applied across a selected resistor, a vapor bubble grows in that particular channel and fluid bulges from the channel orifice. At that stage, the bubble begins to collapse. The fluid within the channel retracts and separates from the bulging fluid, which forms a droplet moving in a direction away from the channel orifice and towards the receiving medium. The channel is then re-filled by capillary action, which in turn draws fluid from a supply container. Operation of one type of a thermal fluid ejector, a thermal ink jet printers, is described in, for example, U.S. Pat. No. 4,849,774.
One particular form of thermal fluid ejection system is a thermal ink jet printer described in U.S. Pat. No. 4,638,337. That ink jet printer includes a reciprocating carriage and has a plurality of printheads, each with its own ink supply cartridge, mounted on the reciprocating carriage. The nozzles in each printhead are aligned perpendicular to the line of movement of the carriage. A swath of information is printed on the stationary recording medium. The stationary recording medium is then stepped, perpendicularly to the line of carriage movement, by a distance equal to or less than the width of the printed swath. The carriage is then moved in the reverse direction to print another swath of information.
The ejecting nozzles of a fluid ejector head need to be periodically maintained, for example, by periodically cleaning the orifices when the fluid ejection system is in use, and/or by capping the fluid ejector when the fluid ejection system is not in use or is idle for extended periods. Capping the fluid ejector head prevents the fluid in the fluid ejector head from drying out. The fluid ejector also needs to be primed before it can be used. Priming the fluid ejector head ensures that the fluid ejector channels are completely filled with fluid and contain no contaminants or gas bubbles.
Periodically, priming the fluid ejector head can also be done to maintain proper functioning of the nozzles. Maintenance and/or priming stations for the fluid ejector head of various types of fluid ejection system are described in, for example, U.S. Pat. Nos. 4,855,764; 4,853,717 and 4,746,938 while removing gas from the ink reservoir of a fluid ejector head during printing is described in U.S. Pat. No. 4,679,059.
A conventional priming operation usually involves applying a sudden vacuum to the nozzles of the fluid ejector head through at least one priming element to withdraw fluid from the fluid ejector head through the at least one priming element and into a waste container. The full pressure of the vacuum is applied suddenly and over a period of relatively short duration.
The conventional priming operation is normally used to prepare newly installed fluid ejector heads or fluid ejector heads connected to newly installed fluid supply tanks, as well as to maintain already-installed or primed fluid ejector heads. This priming technique has worked well with older conventional fluid ejector head designs. However, as the resolution of the fluid ejector heads has risen, the newer fluid ejector heads are not amenable to this conventional priming technique. This appears to be due, at least in part to the finer mesh filters and somewhat more intricate channels used on higher resolution fluid ejector heads. As a result, several priming operations may need to be performed to successfully prime such higher resolution fluid ejector heads. This can be annoying to users, as the loss in time is counterproductive and multiple priming operations in rapid succession could, under some circumstances, exceed the ink delivery rate of the fluid supply tank, thus defeating the purpose of the priming operation, or, at the least, significantly raising the operating costs of the printer, overwhelming the waste fluid system of the maintenance station, or the like.
This invention provides systems and methods that apply a gradually increasing negative pressure profile to charge newly installed fluid ejector heads.
This invention separately provides systems and methods that apply a gradually increasing negative pressure profile to charge fluid ejector heads with newly installed fluid supply tanks.
This invention separately provides a method of suddenly applying the full value of the negative pressure profile and sustaining this negative pressure for a relatively short interval to prime a fluid ejector head for print quality defects and air bubble relief, as well as to unclog nozzles clogged with dirt or dried ink debris.
In various exemplary embodiments of the systems and methods according to the invention, a longer, gentler priming profile is achieved by allowing a vacuum pump to gradually generate the maximum profile vacuum while keeping open a valve that is functionally situated between the vacuum pump and the fluid ejector head.
In various exemplary embodiments of the systems and methods according to the invention, a longer, gentler priming profile is achieved by gradually opening at least one valve that is functionally situated between the maximum profile vacuum and the fluid ejector head.
These and other features and advantages of this invention are described in, or are apparent from, the following detailed description of various exemplary embodiments of the systems and methods according to this invention.